Sam Rockwell's vulgar ad-lib on 'SNL' has Twitter buzzing

When Golden Globe-winning actor Sam Rockwell made his “Saturday Night Live” hosting debut Jan. 13, he was probably hoping to wow viewers with his impeccable comedic timing — but they ended up being stunned by his potty mouth instead.

That’s right, the “Three Billboards Outside Ebbing, Missouri” star dropped the F-bomb during his very first sketch.

The cringeworthy incident occurred during a PBS parody skit called “Science Show” that also featured regular “SNL” cast members Cecily Strong and Mikey Day. Rockwell plays a Bill Nye-esque science teacher who attempts to teach two of his more intellectually challenged students about the wonders of science using experiments.